The present invention is directed towards shock protectors for micro-mechanical systems.
Fiber optic networks have the potential for greatly increasing telecommunication bandwidths and data rates. The demand for increased capacity continues to grow, especially as more and more information is transmitted across the Internet.
One limitation of fiber optic networks as currently implemented is their inability to directly switch optically encoded packets of data from a fiber on a source network or network node to a fiber on a destination network or network node. Instead, optically encoded data are dropped from the source network fiber, converted to electrically encoded data, switched to the destination network using conventional electronic switches, converted back into optically encoded data, and injected into the destination network fiber.
Micromachined mirror arrays offer the ability to directly switch optically encoded data in devices, known as all-optical cross connect switches, from a source fiber on a source network to a destination fiber on a destination network without having to convert the data from optical to electronic and back again. For such mirror arrays to be commercially useful, they must be able to cross connect approximately 1000 input fibers with an equal number of output fibers in a compact volume. This can be achieved with mirrors that can be densely packed together and that are rotatable by relatively large angles in an arbitrary angular direction.
Recent developments in the field of microelectromechanical systems (MEMS) allow for the bulk production of microelectromechanical mirrors and mirror arrays that can be used in all-optical cross connect switches. MEMS-based mirrors and mirror arrays can be inexpensively designed and produced using conventional tools developed for the design and production of integrated circuits. Such tools include computer-aided design, photolithography, bulk and surface micro-machining, wet and dry isotropic and anisotropic etching, and batch processing. In addition, deep reactive ion etching methods (DRIE) allow silicon devices to be produced having high aspect ratios (xcx9c20:1) that rival those that can be achieved using the prohibitively expensive lithography, electroplating and molding process which requires access to a synchrotron radiation source.
A number of microelectromechanical mirror arrays have already been designed for use with MEMS production processes and techniques. In U.S. patent application Ser. No. 09/779,189 of Nasiri, filed on Feb. 7, 2001, and hereby incorporated by reference in its entirety, a mirror is mounted on a support post mounted on a freely moving plate. In Nasiri, two orthogonally oriented pairs of rotatable actuators are coupled to the freely moving plate by gimbal springs. By properly coordinating each pair of actuators, the mirror can be rotated without displacement under ideal conditions.
Although the Nasiri application shows improved ability to manipulate the mirror rotation without displacement, the performance of similar configurations can be greatly improved by paying special attention to the system used for transmitting rotation from the actuators to the freely moving plate. U.S. patent application Ser. No. 10/225,081 of Starr et al, filed on Aug. 20, 2002 and hereby incorporated by reference in its entirety, discloses special gimbal springs and lever arms for coupling the actuators to a gimbaled platform, which is herein denoted a pedestal.
What has been missing from previous mirror rotation systems are means to reduce the detrimental effects of shock loads to the system. Such loads can lead to large out-of-plane displacements of the pedestal that overly strain the gimbal springs (and in some embodiments also actuator springs) and/or lead to unnecessary vibrations in the system.
The present invention discloses structures that can reduce the out-of-plane displacements of a pedestal that is suspended by gimbal springs attached to linkage arms. One embodiment of the invention includes a stop that is located below the pedestal, between the pedestal and a lower surface. The stop prevents the pedestal from impacting the lower surface. In most embodiments, the stop also reduces the maximum strains experienced by the gimbal springs, and in many circumstances, the actuator springs.
Another embodiment of the present invention includes a shock absorber that extends from at least one linkage arm beyond where the linkage arm attaches to the gimbal spring. In case of excessive rotation of an actuator connected to the linkage arm, or exposure to a sudden acceleration, the shock absorber impacts the lower surface and resists further rotation of the actuator.
These shock protectors can be used either independently or in combination with each other or with other mechanisms to limit the out-of-plane displacement of the pedestal.
Some embodiments of the present invention also provide a method for increasing heat transfer from a mirror coupled to a pedestal suspended by gimbal springs over a lower surface. The method includes the provision of a solid heat-conduction path to the lower surface, wherein the heat-conduction path is located within 3 xcexcm of the pedestal. By locating a solid heat conduction path so close to the pedestal, the thermal resistance associated with the gap is decreased, thereby enhancing the heat transfer. In various embodiments the inclusion of a stop located so closely below the pedestal serves as the desired solid heat-conduction path.